F-23 Free Communication/Poster - Bone: June 1, 2007 1:00 PM - 6:00PM ROOM: Hall E
Previous studies have found that serum parathyroid hormone (PTH) increases in response to relatively short (<60 min), intense bouts of exercise, possibly as a result of decreases in serum calcium. A recent investigation found that 50 minutes of lower intensity exercise at 85% of ventilatory threshold (VT) did not stimulate an increase in PTH. Whether longer bouts of lower intensity exercise also stimulate an increase in PTH is not known.
PURPOSE: To determine the effects of 2 hours of moderate intensity cycling on serum PTH and calcium, and to determine whether changes in PTH and calcium were related to dermal calcium loss.
METHODS: Competitive male cyclists aged 20–45 were recruited (n=20). Subjects underwent VO2max testing on a cycle ergometer. On a separate day, subjects then exercised on the cycle ergometer for 2 hours at workloads that varied from 60-75% of their VT power. Serum PTH and calcium were measured before and after the 2 hour exercise bout. Dermal calcium loss was estimated using a patch collection technique and correcting changes in body weight for water consumption during exercise.
SUMMARY OF RESULTS: Corrected serum calcium was found to decrease from 9.3 ± 0.3 to 8.8 ± 0.5 mg/dl (mean ± SD; p<0.01) despite an increase in PTH from 40.6 ± 15.6 to 69.5 ±25.5 pg/ml (p<0.001). Dermal calcium loss was estimated at 138.0 ± 71.9 mg for the 2-hour exercise bout. Neither the change in serum calcium nor the dermal calcium loss was significantly related to the increase in PTH.
CONCLUSION: The study demonstrated that prolonged moderate intensity exercise disturbs calcium homeostasis and leads to increases PTH and decreases serum calcium. These responses could contribute to the relatively low bone mineral density that is sometimes observed in endurance athletes.